


Mabel's Erotic Fam-Fiction

by SprucePines



Category: Gravity Falls
Genre: F/M, Incest, Sibling Incest, Twincest
Language: English
Status: Completed
Published: 2015-03-19
Updated: 2015-04-08
Packaged: 2018-03-18 15:46:53
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 2
Words: 4,334
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/3574976
Author URL: https://archiveofourown.org/users/SprucePines/pseuds/SprucePines
Summary: <blockquote class="userstuff">
              <p>Mabel has taken to writing erotic fiction to try and quell her feelings for Dipper. Dipper discovers her stories and learns the truth.</p>
            </blockquote>





	1. Chapter 1

**_I wrap my arms around him as he kisses me. His tongue presses against my lips, begging to be let in. As he grinds his groin against me, I open my mouth to moan and his tongue finds mine. Before I know it, his hands reach up my skirt and pull my panties down. I hear the unmistakable zip of his pants and soon I feel him pressing against me. He pulls his lips away and looks into my eyes. God, I could lose myself in them. He opens his mouth to speak and I hear him hungrily say my name—_ **

“MABEL!” Dipper’s voice called through her bedroom door. Mabel jolted in her chair, her flailing fingers suddenly turning her name on screen to **_Maipawugrt8ow_**. She closed her eyes and calmed her breath before answering her brother.

“What?”

“Have you forgotten what time it is? We gotta go.”

Mabel checked the clock in the corner of her screen. _Shoot!_ 6:48. If she didn’t hurry, they’d be late to the movie. She quickly deleted her accidental typo and looked over what she had written. She knew it was wrong having these thoughts; knew she could never even think of acting on them. But this was the best option she could come up with. This way, her perverted fantasies get transferred from her overactive imagination onto a text document and out of her mind.

The slight twinge of guilt she feels as she saves her work is commonplace to her now. Closing the program she scrolled through her file folder. How many cute, sweet, fluffy, romantic, suggestive, titillating, salacious, and downright nasty stories had she written? Too many, she knew, and they were all there on her hard drive for her to either add to when another forbidden fantasy came to her or, sometimes, for her to revisit on the evenings when she felt especially nasty.

“MABEL!” Dipper’s voice called again, from further away this time. She clicked closed the window, rose from her chair, and quickly left to join her brother.

Dipper stood at the front door, watching as his twin sister bounded down the stairs. “Finally,” he said with a sigh. “What kept you?”

“Oh, pfft, you know,” she said, waving her hand dismissively, “social media, cat videos, the usual.”

Dipper shook his head. Of course she’d be distracted by those things. In fact, he noticed that she’d forgotten something. “Uh, Mabel,” he said, “your sweater?”

Her eyes widened. “Oh, fudge,” she said as she turned on her heel.

“Wait,” Dipper said. “I’ll get it; you just get your shoes on.”

“Oh, uh, okay,” she said. “It’s lying on the bed.”

“Right,” he said as he climbed the staircase. He entered his sister’s room and sure enough, there was her sweater lying on her bed. He looked down at the design. _Why would anyone want a sweater with a picture of a sweater on it?_ He picked it up off her bed and turned to the door when he noticed something in his peripheral vision.

He turned to see Mabel’s computer screen still on. Sighing, he stepped up to the desk and took the mouse. As he moved the pointer across the screen, he noticed a file folder near the lower corner, labeled “Mystery Twins.” Unable to contain his curiosity, he double-clicked it. A moment later, a window opened filled with text documents.

He looked through the filenames. “Camping Trip,” “Nature Hike,” “Puppet Show.” _Mabel must be keeping a computerized journal,_ he thought. But then some of the others caught his attention. “Mistletoe Kisses,” Midnight Skinny Dip with Dip,” and…“Touching My Bro-bro’s No-no.” _What? What is…WHAT?!_

Knowing time was short, Dipper reached into his pants pocket and pulled out a flash drive. _Always knew it was a good idea to keep one handy._ He plugged the drive in and copied the folder over. Thankfully, it only took a few moments. He pocketed the drive, clicked “shut down” on Mabel’s computer, and made his way back downstairs.

“Hey, Dipster,” Mabel said when he reappeared in the entryway, “what kept ya?”

Luckily, he was ready with a half-truth. “I saw that you left your computer on, so I shut it down for you. I took a few seconds to make sure nothing important was running first.”

“Awww,” Mabel said, wrapping her arms around Dip’s neck and pulling the two of them together, cheek-to-cheek. “That’s why I’m so happy to have you for a brother. You’re always looking out for me.”

Dipper managed a smile, though some of those filenames kept troubling him. He gently pushed his sister away, saying, “Come on, we gotta get going.” He handed Mabel her sweater.

“Say, Dip-dop, you think maybe _I_ can pick the movie this time?”

“Mabel, all you ever want to see are those silly romantic comedies.”

“And you keep insisting on those sci-fi movies. Come on, Dip.”

“Maybe next time, alright?”

Mabel huffed. “Alright,” she muttered as they walked out the door.

*********

**_Dipper leads me to his room. It’s not like I haven’t been in there hundreds of times before, but there’s something in the way he’s looking at me that tells me that this time is something different. Something special. He opens the door, not bothering to switch on the light. I cross the threshold and he closes the door behind us, surrounding us in darkness. I feel my brother’s hands on my shoulders, guiding me carefully to a specific spot. My heartbeat grows louder in my ears with each second._ **

**_Dipper steps away from me and a few seconds later, the lights come on. Instinctively, I glance around, then at my feet, then above my head. That’s when I see it, hanging down from Dipper’s ceiling fan._ **

**_Grinning widely, Dipper steps towards me. Somehow his steps sync up perfectly with my pounding heart. He reaches up and laces his fingers behind my neck and slowly pulls me in for—_ **

_Oh, my God!_ Dipper thought as he quickly clicked the document closed. _What the hell? How can Mabel write something…like_ that _?!_

He scrolled through the list again, concerned at just how many files there were. _How long has she been doing this?_ Taking a deep breath, he selected another file and opened it.

**_Our dancing around the room quickly leads us towards my bed. As my legs brush up against it, I make a not-so-subtle show of falling over onto it, pulling Dipper down with me. In just a moment or two, we’re both tangled up in each other, giggling like we were little kids again. I lean in and kiss him, silencing the both of us. My eyes close as he returns the kiss, and I feel his hand slowly move up my thigh. I shudder as his hand comes closer and closer, his fingers deftly sliding down my panties and into my—_ **

Dipper tore his eyes away from the screen. He wasn’t sure which was worse, reading a story where he and his twin sister were far more than just siblings or that his curiosity was clamoring for more. His heart was pounding in his chest. For the first time in a long time, he was afraid. But this wasn’t a vengeful lumberjack’s ghost, or a triangular dream demon, or even a white-haired faux-psychic twerp. This was his sister! As much as he didn’t want to say it, even to himself, it seemed that Mabel’s romantic inclinations had turned their way to him.

Against his better judgment, he clicked open one more story.

**_Our clothes are all bunched up on the floor. Dipper lays back on his bed, his “Little Dipper” standing at full attention. I feel his eyes explore my own nakedness and I see his erection twitch. I climb on top of him and I press my mouth to his. Our tongues dance with each other while our hands grasp and squeeze. I reach down and wrap my fingers around his cock and I both hear and feel him moan. I break off our kiss and crawl down until my face is hovering over his hard on. I glance up into his eyes and the eagerness I see in them matches my own. Without a word, I open my lips and take him into my mouth._ **

Dipper sat back in his chair, looking again over the words he just read. Now he _knew_ he was in serious trouble. His breathing had become heavy, and he didn’t need to look down to know that he was tenting his pants. He put his head in his hands. _Oh, man…what do I do now?_

*********

**_Her legs straddle my waist as she climbs atop me. She grins down at me as my hands make their way up her body to her chest. I gently squeeze her breasts and I hear Mabel coo softly. She rocks her hips, rubbing herself against me. The sensations drive us both wild. She lifts herself up and I feel her hand take hold of me, lining the both of us up. A moment later, she lowers herself back down and her pussy envelops my cock. I sigh as I sink deeper and deeper into her, until she’s completely taken me in. She lowers her face next to my ear and whispers my name—_ **

“DIPPER!” Mabel practically shouted through his bedroom door, shocking him. He quickly spun in his chair to face the closed door.

“Geez, Mabel, way to give a guy a heart attack!”

He heard his twin giggle. “Fair’s fair. Serves you right for scaring me last time. It’s time to go.”

He glanced at the time. “Oops,” he said. “Be right there.”

He looked over what he’d typed and felt a pang of guilt. He really shouldn’t be doing this. Really, he shouldn’t have gone through Mabel’s computer in the first place. He couldn’t really blame her for this, much as he’d like to. He’d done it to himself. He and his own curiosity. He saved his work and closed down his computer.

 _So what_ do _I do now?_ he thought to himself as he approached his bedroom door. He opened it and was greeted by his twin sister, smiling ear-to-ear.

“There ya are!” she said. “Come on, let’s go!” She turned and bounded down the stairs.

The image of her standing there, smiling, imprinted itself in Dipper’s mind and he found himself smiling, too. _Maybe it isn’t really that bad. After all, she’d been writing all these stories and she still manages to keep it together. There’s no reason why I can’t, too. And maybe—_

He stopped himself, not sure if he should even finish the next thought.

 _Maybe…we actually_ could _become something more than just siblings._

He waited for the rational side of his mind to butt in, scolding him for even entertaining such a preposterous idea. However, it didn’t happen. Instead, he felt a warmth fill him when he thought of he and Mabel, together. And that made him smile even wider as he followed his sister down the stairs.

“Hey, Mabel,” he said when he reached the entryway.

“Yo-yo, bro-bro,” she replied.

“Why don’t you choose the movie this time?”

Mabel’s eyes, and her smile, doubled in size. “Really?”

“Sure,” he said, “anything for my favorite Mabel.”


	2. Chapter 2

“Well?” Dipper asked as they approached the box office. “Which movie do you want to see?”

Mabel still couldn’t believe her brother was letting her choose this time. She looked at the multiplex’s offerings. The current releases included a couple dramas, a gross-out comedy, the latest helping of Michael Bay-splosions. In truth, there was really only one she had her eyes on, but would he agree to it?

“Um, how about that one?” she asked, pointing to the poster for a new romantic epic. Dipper looked at the poster, which depicted the latest power couple out of Hollywood embracing against the backdrop of the American Revolution. “I mean, we don’t have to if you don’t want—“

“Two tickets, please,” Dipper said as he stepped to the clerk. Mabel was surprised; he didn’t even hesitate. She stared after him as he paid the girl behind the counter and turned to face her again. “What’s wrong?” he asked. “I have something on my face?”

Mabel shook her head to reset her brain a bit. “No, no, I’m just…I didn’t think you’d really go for this movie.”

“I said you could pick this time, right?” She nodded her head. “Well, now you know I really meant it.”

Mabel couldn’t help but smile. Even given how often she’d had to let Dipper choose the movie, his readiness to see a genre he really didn’t care for warmed her heart. It almost made this outing seem like a date.

_Whoa, get your head back down to earth, Mabel-fo-fable. This is Dipper, your twin brother, we’re talking about here. There’s no way this is going to turn into one of your stories._

“You want some popcorn or candy?” Dipper asked. “My treat.”

_But I suppose there’s nothing wrong with imagining it that way…later. In your room. In front of your computer._

After buying their snacks Dipper led Mabel to the theater, which sat about half full. They picked some seats near the middle and settled in just as the previews began to play.

*********

Mabel sat in silence as Dipper drove them home afterwards. All through the movie, she kept feeling as though someone were looking at her. She glanced at her brother, but his eyes always seemed focused on the screen. She found it difficult to turn away again. She’d allow her eyes to wander a little bit around his face, imagine what it would feel like to run her hand through his hair or feel his stubble on her fingertips. More than once, she let her eyes fall upon his lips and wonder if kissing them in real life would be anything like how she kept imagining it in her fantasies. She only managed to tear her eyes away when she thought he might catch her ogling him. _Save your perverted mind for after, when he’s not around._

Now, in the car, something occurred to her that she’d neglected. Something important.

“Hey, Dip?” she asked.

“Yeah, Mabes?”

“Thanks. For letting me pick the movie. And for the candy.”

“Well, it was really only fair. How many times had I chosen?”

“I’d lost count after movie night number 3578,” she said, playfully sticking her tongue out.

Dipper laughed at her joke. “And promise not to laugh?”

She nodded.

“I actually…kinda enjoyed it. It makes me feel a little stupid for saying no so many times.”

“Well, you look a little stupid.”

He gave her a wry smile. “Takes one to know one.”

Giggling, Mabel blew a raspberry at Dipper, which he returned with a laugh of his own. After they both calmed back down, she said, “But really, Dip. Thank you. It actually meant a great deal to me.”

He glanced sideways at her and smiled warmly. He reached over and took her hand in his, squeezing it gently. There was something in the act that made her heart skip a beat and her breath catch in her throat.

“You’re welcome, Mabes,” he said. She looked into his eyes and thought she might have seen…something in the way he looked at her. It was only there for an instant before it was gone and his attention was back on the road. She puzzled over it for the rest of the ride home, but she noticed that he hadn’t taken his hand off of hers.

*********

**_As I reach for another handful of popcorn, his hand brushes against mine. I feel a tingle at his touch and I gasp. Part of me hopes he didn’t hear it while another part wishes that he had._ **

**_“Mabel?” I hear him say. Hesitantly, I raise my eyes and find Dipper staring at me. His hand gently grips mine and he pulls me towards him. Before I know what’s happening, his lips have found mine. I steal a glance around the theater. The handful of people there are all watching the movie. Meanwhile, the rear where we sat was otherwise vacant._ **

**_I return my brother’s kiss, my hand reaching up and rubbing the stubble on his cheek. His hand reaches over and runs a path over my thigh, my hip, my stomach, before settling on my breast. I grunt softly as his fingers work over my flesh through my sweater. His actions embolden me and I reach my own hand over, placing it first on his chest, where I feel his heart beating. I reach further down, over his stomach before I come to the growing bulge in his jeans. I hesitate for only a moment before I plunge ahead and gently cup his—_ **

“NUTS!” came the cry from Dipper’s room, bringing Mabel out of her latest writing.

“You alright in there, Dipper?” she asked through the wall.

“ _I’m_ alright, but I’m late to meet the study group for coffee.” In a matter of moments, she heard shuffling from Dipper’s room before it migrated to the hallway, down the stairs and finally, after a quick shout good-bye, out the front door. After hearing his car start up and pull away, she turned her attention back to her computer screen.

As she thought over just what sexy shenanigans her brother’s and her fictional counterparts could get up to in a dark movie theater, she felt the unmistakable call of nature. After coming back out of the bathroom, she happened to look towards Dipper’s bedroom door, slightly ajar, and notice a light coming through. Curious, she stepped closer and saw that in his haste, Dipper had neglected to shut down his computer.

Remembering how he had shut her own computer off before, she decided it only fair to return the favor. Entering his room, the first thing she noticed was the smell. The room definitely smelled of boy. But not just any boy; the room smelled of Dipper. That one detail made it almost intoxicating to her. _Settle down, girl. Just do what you came in here to do and get out before you go and do something silly._

She carefully navigated her way through the minefield of discarded clothes to Dipper’s desk. Taking the mouse in hand, she looked to the screen and saw a window sitting open. Inside it were a few word processing documents and a subfolder.

 _Huh. He must have been writing something, too. That’s a neat coincidence._ Her eyes followed the pointer as it crossed the screen, passing over the window right near the subfolder. When it did, Mabel saw that the folder’s name was the same as hers. Unable to stop herself, she clicked it open and her eyes grew wide as she saw her stories fill up the window.

_What the—? What’s Dipper doing with these? Did he…did he read them? Oh, my god. Dipper, how could you?!_

Her lip trembled in a mixture of anger and embarrassment. She felt betrayed and exposed. Her own brother had not only found her fantasy fiction, but had copied them to his own computer, for what use she didn’t know.

 _Hey, wait a sec._ A tiny rational part of her mind managed to speak up. _What’s the most recent story in the folder?_

She scanned through the dates before she found it. _That’s the one I was working on when he went after my sweater and shut my computer down. And shortly after that was when he let me pick the movie._

_Which might mean…_

_It couldn’t be._

_Could it?_

She clicked back to the main folder and looked through the files. There weren’t very many, only a few. She clicked open the latest file and read.

**_The fire in the fireplace burns brightly, bathing the both of us in orange hues. I carefully caress her face, marveling for what seems like the millionth time how smooth her skin is. Mabel grins at me and I can’t help myself anymore. I bring her lips to mine and we fall together to the floor in each other’s arms._ **

**_Mabel’s the first to start undressing, lifting her sweater over her head in one quick motion. Underneath it, a lacy bra teases me with what its cups hold inside them. I wrap both hands around her breasts. Her body feels hotter than the fire. While I unclasp and free her breasts, she grabs my shirt and pulls it off of me before leaning back in to kiss, our now bare flesh pressed together._ **

**_My hands roam from her breasts down to her ass. I squeeze and pull down, grinding her onto me. I know she can’t help but feel how hard I am. And we both know that she’s the one who does that to me._ **

Mabel sat back in Dipper chair as she finished reading.

_Well…I guess that settles that question._

_Now the question is, what do we do about it?_

Mabel mulled the question over for a few moments before looking again at the words on screen. Rereading the last sentence, she nodded her head and began to type.

*********

Dipper quietly entered the house a few hours later. It turned out he wasn’t the only one late for coffee, so he didn’t feel quite so bad. He kicked his shoes off and climbed the stairs to his room. Dropping his jacket to the floor he sat at his computer desk and jostled the mouse to wake his desktop up. When the screen came on, he found the story he had been working on sitting open.

_Wait a minute. I closed the program._

_Are you sure?_

_Positive, I distinctly remember saving and closing it before I stood up._

_So why is it open?_

_I don’t know. Unless…_

Dipper froze. It could only be sitting open if someone else opened it. And right now there was only one other person in the house with him.

_Oh, shit._

He knew that she knew he was home. Even being quiet coming in, she could hear his car from half a block away on its approach. _So why hasn’t she come in here and started shouting at me or anything?_

He looked through the document, rereading his words…until he found something he didn’t remember typing. He read on:

**_Never breaking our kiss, she reaches down and undoes her skirt, pulling it away from between our bodies. I feel her fingers work in between us and hear the telltale zip of my jeans. I reluctantly release my hold on her to push them down._ **

**_A moment later, we each reach for the other’s underwear, pulling them down and away. Now completely exposed, she looks at my rock hard cock while I look at her pussy. Just looking at her inviting body seems to make my erection grow even thicker. She gently takes it into her hand, her touch making me shudder. I lose the ability to talk for a moment. Mabel, however, knows just what to say._ **

**_“Hey, Dipper,” she said, “if you’re up for a little ‘collaboration,’ I’m waiting in my room right now.”_ **

Dipper had to reread that last sentence before he realized what it meant. He turned and stared at the wall between their rooms, then back at the screen.

**_“I’m waiting in my room right now.”_ **

Dipper closed the document and walked out of the room. He stood before Mabel’s door and, after a gulp, gently knocked on the door.

“Come in.”

Dipper turned the knob and entered Mabel’s room.

*********

**_Mabel gasped as Dipper started to push his cock inside her. Until now, she’d only imagined how it would feel, used her fingers or a dildo and dreamed it was her brother entering her. She couldn’t imagine how hot his erection would feel. She felt like she would melt from the heat, but she craved more. She wrapped her legs around her brother’s waist and pushed him all the way inside of her._ **

**_Likewise, Dipper wasn’t prepared for how wonderful it would feel. The soft feel of her pussy gently teased his own sensitive flesh. He could have cum right then and there before his sister’s legs wrapped around him and pressed him all the way in. They both sighed as he sank to the hilt._ **

**_Dipper looked down at Mabel on her bed. Even though he’d only begun having these thoughts for her for a very short time, he couldn’t imagine anyone other than her for him. He leaned down and kissed her deeply as he began to thrust._ **

**_“Oh, god,” Mabel said as her brother began to slowly fuck her. His cock gently rubbed against her insides, sending shocks of electricity through her body. It took all she had not to spasm wildly. As it was, she couldn’t suppress every twitch, which rubbed her against Dipper even more._ **

**_Dipper knew he wouldn’t last very long. Mabel’s twitching teased the head of his dick, which only drove him closer to the edge. “Mabel, I—I’m gonna—“_ **

**_Mabel tightened her grip with her legs, trying to force him deeper and deeper into her while her hands gripped his shoulders. Unable to stop himself, Dipper began to thrust as fast as he could, his skin smacking against hers. Their voices devolved into a series of guttural grunts and moans until just before they both came together and they each screamed the other’s name:_ **

“DIPPER! MABEL!” their mother’s voice called from downstairs. “It’s time for dinner!”

The twins looked at the time.

“Whoops,” Mabel said.

“We can finish this up a little later,” Dipper said, rising from his chair.

“Okay. Say, Dip.”

“Yeah?”

Mabel began to play with the locks of her hair. “You think you might want to collaborate again? Say, maybe Saturday?”

Dipper grinned as he leaned down and gave his sister a long kiss on the lips.

“Absolutely. As far as I’m concerned, we’re co-authors from now on.”


End file.
